Why do the tugs pull the planes forward for so long like that? Can't the planes' engines handle it themselves?

If you're ever around ATL, you'll see a whole fleet of "minitugs" and "supertugs". Maintenance facilities for ExpressJet and AirTran are on the north side, Delta on the east side, and spare Delta parking on the north and south sides. It is much more cost efficient to pick these planes up with a tug and ramp agents and tow them around the airport, rather than paying mechanics or pilots to burn fuel and taxi them around.

I just took a series of five commercial flight segments last week, making a big swing around the southwest states, and I noticed tugs in use a lot, too. In almost every case, the planes I was on were pushed back and then tugged all the way out to where the taxiways officially start.